Decorative laminating paper is an element of a decorative thermoset surface, which is used with preference for finishing furniture surfaces and for laminate floorings. Laminate is the term used for materials in which wood and paper, for example, are pressed with resin. The use of special synthetic resins results in extraordinarily high resistance of the laminates to scratching, impact, chemicals and heat.
The use of special-purpose papers (decorative laminating papers) permits the production of decorative surfaces, where the decorative laminating paper serves not only as facing paper for unattractive wood material surfaces, but also as a carrier for the synthetic resin. The requirements imposed on decorative laminating paper include, for example, hiding power (opacity), light-fastness (greying resistance), colour-fastness, wet strength, impregnability and printability.
In principle, a pigment based on titanium dioxide is eminently suitable for achieving the necessary opacity of the decorative laminating paper. As a rule, a titanium dioxide pigment or a titanium dioxide pigment suspension is mixed with a fibre suspension during paper production. The interactions between the individual components (fibres, pigment, water) contribute to formation of the paper sheet and determine the retention of the pigment. The term retention refers to the retention of all inorganic substances in the paper during production. In addition to the pigment and fibres used as feedstock, auxiliaries and additives are generally also used. These may affect the mechanisms of interaction between the fibres, the pigment and the water.
A number of titanium dioxide pigments exists for applications in decorative laminating paper. Alongside the most important properties, such as retention and opacity (hiding power), the greying resistance also plays a decisive role.
It is generally known that titanium dioxide is photochemically active. When exposed to UV radiation in the presence of moisture, decorative laminating paper pigmented with titanium dioxide displays increasing greying. To avoid this problem, the surface of the pigments is treated with various substances, for instance with Al2O3 aquate and a colourless metal phosphate (U.S. Pat. No. 3,926,660), with zinc phosphate (U.S. Pat. No. 5,114,486), with cerium phosphate and aluminium phosphate (GB 2 042 573), or only with aluminium phosphate (EP 0 753 546 A2). DE 15 92 873 describes a method for improving the light-fastness of pigments, where calcination at 600° C. is performed following coating with magnesium silicate.
TiO2 pigments with improved retention properties, having a cores coated with consecutive layers of aluminium oxide phosphate, aluminium oxide and magnesium oxide, are presented in EP 0 713 904 B1, U.S. Pat. No. 5,665,466 and U.S. Pat. No. 5,942,281.
A TiO2 pigment, having a core coated with consecutive layers of zirconium hydroxide or oxyhydroxide, titanium hydroxide or oxyhydroxide, and co-precipitated phosphate and silica, and finally a layer of aluminum oxyhydroxide and magnesium oxide, is shown to protect the organic pigment binder from light and to decrease the loss of gloss in paint in U.S. Pat. No. 6,200,375.
All of the preceding publications, patents, and patent applications are hereby included in their entirety in this application.